JWST MIRI-MRS observations of the Red Rectangle Aromatic infrared band class transformation in the outer nebula

Aims. We characterize the mid-infrared spectrum of the outer regions of the Red Rectangle nebula to probe the carbonaceous dust and molecular content beyond the circumbinary disk.
Methods. We present JWST MIRI-MRS observations of the southwest whisker that were extracted from three distinct environments: the biconical outflow, the whisker itself, and the shadow region outside the outflow. We compare them with an archival ISO-SWS observation of the inner nebula.
Results. The JWST spectra display only classical aromatic infrared band (AIB) emission on a weak dust continuum, with no signatures of the oxygen-rich circumbinary disk mineralogy nor of the rich molecular emission seen at optical wavelengths. The AIBs are predominantly Class A, which is in marked contrast to the exclusively Class ℬ profiles previously reported for the inner regions; there are systematic differences between the outflow and shadow regions that point to environmentally driven polycyclic aromatic hydrocarbon processing.